The present invention relates to a method and a system for quantitative measurement of the handling characteristics of tires and/or vehicle/tire combinations or systems. The present invention is an attempt to relate driver control to vehicle responses under test conditions so that quantitative indications of transient and steady state behaviors are obtained. This is particularly true in regarding driver perceived oversteer and driver perceived understeer behavior. This invention also relates to the quantitative comparison of one vehicle/tire combination with another. This invention also provides a method of correlating a driver's subjective handling ratings of a tire for a particular tire and/or vehicle and the quantitative measured data.
Various methods and techniques have been tried over the years to determine the handling characteristics of vehicles in general and/or tires specifically. One of the most common methods is to have a driver test a vehicle on a test track which subjects the vehicle to a number of different test conditions. The driver may then provide comments and/or subjective rankings concerning performance during braking, cornering, acceleration, wet, rapid maneuvers, etc.
It has therefore been an industry objective over the years to develop a means for testing vehicles, tires, etc., that either eliminates or reduces subjective human differences and relies more on an impartial objective method. Some methods require specific, controlled driven inputs for a single isolated handling test maneuver or for a steady-state maneuver. Some methods attempt to show quantitative results of a particular vehicle response which does not directly relate to a driver's impression of how the vehicle handles. Also various computer models or other models have been developed which represent the handling characteristics of various vehicles or portions of a vehicle including suspensions, tires, etc. These models however are generally limited to steady state handling conditions and have been restricted to the qualitative statement that a vehicle has final understeer or final oversteer characteristics and not to quantitative results.
For example, S.A.E. paper 820456, "Instrumental Objective Tire/Vehicle Handling Testing" by R. J. Strange (1982) sets forth one method of objectively evaluating the handling characteristics of tire/vehicle systems. The method is divided into two portions a steady state and a transient portion. In the steady state portion the speed, Lateral Acceleration and steering wheel angle are measured for constant rate of steer angle while maintaining a constant input speed. From this a ramp steer plot is obtained and an understeer coefficient is calculated which relates to the overall vehicle behavior. The transient conditions are obtained by driving at a constant speed and imparting a step steering input of 140 degrees until the car reaches a steady state attitude. The subjective ratings of the tires by the driver are then compared with the plotted data.
This method alone does not provide analysis and understanding of instantaneous responses of a vehicle/tire system in real world driving situations. For example it does not take into account applied throttle or braking, (acceleration/deceleration) during cornering. The acceleration and deceleration during cornering causes changes in the vehicle/tire handling responses which may cause the driver to make driving corrections. Nor does this method provide for numerous maneuvers such as an "S" curve. In short, the instantaneous actions and responses of the vehicle/tire over any desired test course are not evaluated.